Heavy oil thermal recovery method based on staged injection of supercritical multielement thermal fluid

ABSTRACT

A heavy oil thermal recovery method based on staged injection of a supercritical multielement thermal fluid, comprising: extracting light crude oil in response to detecting that the oil storage stratum having an ignition temperature through preheating the oil storage stratum; increasing a temperature of the oil storage stratum through igniting heavy oil in the oil storage stratum having the ignition temperature; and injecting, sequence to heating the oil storage stratum to a required temperature, a multielement thermal fluid into the oil storage stratum, and extracting crude oil sequence to an operation of closing in. Reaction temperature is increased by heat released by the crude oil during combustion, and a supercritical state of water is reached. The addition of a catalyst can promote the reaction, and therefore, when the temperature drops below a critical point in partial regions, the catalyst can ensure the reaction is continuously and efficiently carried out.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International Application No. PCT/CN2021/141793, filed on Dec. 27, 2021, which claims priority to Chinese Patent Application No. 202011588120.X, filed on Dec. 28, 2020, both of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention belongs to the field of oil extraction, and in particular, to a heavy oil thermal recovery method based on staged injection of a supercritical multielement thermal fluid.

BACKGROUND

In the modern world, a large amount of oil resources is consumed every day. Oil is a kind of non-renewable resource, but people's demand for oil is still growing. With the consumption of light oil resources, the proportion of heavy oil in the oil resources is increasing. Especially for China, where the oil resources are scarce, heavy oil has become an important oil resource. The traditional thermal recovery technology heats the storage stratum to reduce the viscosity of heavy oil, which can only temporarily reduce the viscosity of heavy oil. Therefore, the stratum needs to be continuously heated to maintain a high-temperature state. In addition, the subsequent transportation of heavy oil still requires a lot of energy, resulting in the problems of low production efficiency, unsatisfactory viscosity reduction efficiency, unsatisfactory energy efficiency, etc.

SUMMARY

An object of the present invention is to provide a heavy oil thermal recovery method based on staged injection of a supercritical multielement thermal fluid, to overcome the defects in the prior art.

In order to achieve the above object, the present invention adopts the following technical solution.

A heavy oil thermal recovery method based on staged injection of a supercritical multielement thermal fluid includes the following steps:

-   -   S1, extracting light crude oil in an oil storage stratum in         response to detecting that the oil storage stratum having an         ignition temperature through preheating the oil storage stratum;     -   S2, increasing a temperature of the oil storage stratum through         igniting heavy oil in the oil storage stratum having the         ignition temperature; and     -   S3, an injecting, sequence to heating the oil storage stratum to         a required temperature, a multielement thermal fluid into the         oil storage stratum, and extracting crude oil sequence to an         operation of closing in.

Further, the method further includes: injecting a thermal fluid having steam and a catalyst into the oil storage stratum to heat the oil storage stratum to the ignition temperature or higher; and injecting a thermal fluid having steam and a flame-retardant gas to combust the oil storage stratum and increase the temperature of the oil storage stratum.

Further, the multielement thermal fluid used includes a mixture of water, a catalyst, and a hydrogen donor.

Further, the method further includes: repeatedly injecting, when the temperature of the oil storage stratum is lower than a reaction-requiring temperature, the thermal fluid having steam and the catalyst to heat the temperature of the oil storage stratum to the reaction-requiring temperature.

Further, a combustion-supporting gas used includes air, enriched oxygen, or pure oxygen.

Further, the catalyst includes a water-soluble salt, an oil-soluble salt or nanoparticles of a transition metal.

Further, the hydrogen donor includes tetralin, methane, formic acid, methyl formate, dihydroanthracene, alcohols and naphthenic straight-run diesel, CO, or CH₄.

Further, the water is injected in a state as mixture of low-temperature water, water vapor, or supercritical water.

Further, an injection well and an extraction well are formed as a single well, or the injection well and the extraction well are disposed separately.

Compared with the prior art, the present invention has the following beneficial effects.

According to the heavy oil thermal recovery method based on staged injection of the supercritical multielement thermal fluid of the present invention, an oil storage stratum is preheated to enable the oil storage stratum to have an ignition temperature, and light crude oil in the oil storage stratum is simultaneously extracted; heavy oil in the oil storage stratum having the ignition temperature is ignited to increase the temperature of the oil storage stratum; and a multielement thermal fluid is injected into the oil storage stratum, and crude oil is extracted after a well operation of closing in. Reaction temperature is increased by heat released by the crude oil during combustion, and a supercritical state of water is reached, such that load of a ground heating device can be reduced. Use of the underground heavy oil which is difficult to extract as fuel realizes the purposes of fully utilizing heavy oil resources and saving energy. The addition of a catalyst can promote the reaction of the supercritical multielement thermal fluid, and therefore, when the temperature of the supercritical water drops below a critical point in partial regions at certain time points, the catalyst can ensure that an aqueous pyrolysis reaction is continuously and efficiently carried out, thereby improving the modification effect and expanding the modification reaction sweep region. The heavy oil thermal recovery method based on staged injection of the supercritical multielement thermal fluid of the present invention has a higher reaction efficiency, a better reaction effect and the catalytic activity, can supplement heat through self-heating, makes full use of the underground heavy oil resource, and can reduce a carbon deposit.

Further, when the temperature of the oil storage stratum is lower than the ignition temperature, the thermal fluid formed by steam and the catalyst is repeatedly injected to enable the temperature of the oil storage stratum to reach the ignition temperature. Heat released by the crude oil in the oil storage stratum during combustion is fully used, such that the load of external heating can be reduced.

Further, the multielement thermal fluid is doped with a combustion-supporting gas, facilitating combustion and heating.

Further, the water is injected in a state as a mixture of low-temperature water, water vapor, or supercritical water. When the water enters a supercritical state, oxygen can be mutually soluble with the supercritical water, showing strong oxidizability, such that a reaction between the heavy oil and the oxygen can be promoted.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating a well placing structure in an embodiment of the present invention.

In the FIGURE: 1, cover stratum; 2, injection well; 3, oil storage stratum; 4, extraction well; and 5, understratum.

DESCRIPTION OF EMBODIMENTS

The present invention will be further described in detail below with reference to the accompanying drawings:

A heavy oil thermal recovery method based on staged injection of a supercritical multielement thermal fluid includes the following steps.

At S1, an initial extraction and preheating stage: light crude oil is extracted in an oil storage stratum in response to detecting that the oil storage stratum has an ignition temperature through preheating the oil storage stratum.

Specifically, a thermal fluid formed by steam and a catalyst is injected into the oil storage stratum, to heat the oil storage stratum to the ignition temperature or higher.

At S2, an underground combustion and heating stage: a temperature of the oil storage stratum is increased through igniting heavy oil in the oil storage stratum having the ignition temperature.

At S3, a supercritical hydrogen-donated modification stage: sequence to heating the oil storage stratum to a required temperature, a multielement thermal fluid is injected into the oil storage stratum, and crude oil is extracted sequence to an operation of closing in.

The process that heavy oil in the oil storage stratum which has reached the ignition temperature is ignited to increase the temperature of the oil storage stratum, forms the underground combustion and heating stage, in which the heavy oil in the stratum is combusted to increase the temperature of the oil storage stratum.

The multielement thermal fluid used in the supercritical hydrogen-donated modification stage is a mixture of water, a catalyst, and a hydrogen donor. After the multielement thermal fluid is injected into the oil storage stratum, the water in the multielement thermal fluid is heated by the high-temperature stratum to reach the supercritical state, and the heavy oil is extracted after being modified under the action of the supercritical water, the catalyst and the hydrogen donor, thereby improving the crude oil recovery efficiency.

When the temperature of the oil storage stratum is lower than a reaction-requiring temperature, a thermal fluid formed by steam and a catalyst is repeatedly injected to enable the temperature of the oil storage stratum to reach the reaction-requiring temperature.

The multielement thermal fluid is doped with a combustion-supporting gas, and the combustion-supporting gas is air, enriched oxygen, or pure oxygen.

The water is low-temperature water, water vapor, or supercritical water. The catalyst is a water-soluble salt, an oil-soluble salt or nanoparticles of a transition metal, which can effectively reduce the activation energy of the modification reaction and increase the reaction rate. The hydrogen donor is tetralin, methane, formic acid, methyl formate, dihydroanthracene, alcohols and naphthenic straight-run diesel, CO, or CH4.

In the initial extraction and preheating stage, the thermal fluid is formed by steam and the catalyst, with the main purpose to heat the stratum and extract the light crude oil. In the underground combustion and heating stage, the thermal fluid reacts with residual heavy oil in the oil storage stratum for combustion, such that the temperature of the oil storage stratum is increased, and the water may be gradually transformed from steam or hot water into the supercritical state. In the supercritical hydrogen-donated modification stage, the hydrogen donor is mixed in the multielement thermal fluid. When entering the underground high-temperature oil stratum, the low-temperature water may be heated up and transformed into the supercritical state. Finally, the crude oil, the catalyst, the hydrogen donor, and the supercritical water may undergo a modification reaction that is greatly improved in effect compared with that in the first stage. In addition, due to heat absorption of the modification reaction and heat dissipation of the stratum, the underground combustion and heating stage and the supercritical hydrogen-donated modification stage may be repeated according to the actual situation, to achieve an optimal oil recovery effect.

The reaction temperature is increased by the heat released by the crude oil during combustion, and the supercritical state of water is reached, such that the load of a ground heating device can be reduced. Use of the underground heavy oil which is difficult to extract as a fuel may realize the purposes of fully utilizing heavy oil resources and saving energy. The CO produced by insufficient combustion may undergo a hydrothermal replacement reaction to produce H2, which may be used as a hydrogen donor in the third stage. With the rise of the temperature of the stratum, when the water enters the supercritical state, the oxygen can be mutually soluble with the supercritical water, showing strong oxidizability, such that a reaction between the heavy oil and the oxygen can be promoted. Supercritical water has the advantages of good diffusivity, capability of dissolving crude oil, high reaction activity, and the like. Research shows that the viscosity reduction effect of the water in the supercritical state on the heavy oil is greatly improved compared with that of the water in a subcritical state, and a carbon deposit is greatly reduced. In combination with the use of the catalyst and the hydrogen donor, the efficiency and the effect of the supercritical water modification reaction can further be improved. Similarly, the yield of heavy products may further be reduced, and the yield of light products may further be increased. Once the crude oil is converted to the carbon deposit, the crude oil cannot be extracted to the ground, which may also lead to channel blockage in the stratum. Therefore, the supercritical hydrogen-donated oil recovery method in the method provided by the present invention has a higher efficiency and a better effect than the traditional technology. Meanwhile, the addition of the catalyst can promote the reaction of the supercritical multielement thermal fluid, and therefore, when the temperature of the supercritical water drops below a critical point in partial regions at certain time points, the catalyst can ensure that an aqueous pyrolysis reaction is continuously and efficiently carried out, thereby improving the modification effect and expanding the modification reaction sweep region. Therefore, the heavy oil thermal recovery method based on staged injection of the supercritical multielement thermal fluid of the present invention has a higher reaction efficiency, a better reaction effect and the catalytic activity, can supplement heat through self-heating, makes full use of the underground heavy oil resources, has a larger sweep region, and can reduce the carbon deposit.

Embodiment

As shown in FIG. 1 , a heavy oil thermal recovery system based on staged injection of a supercritical multielement thermal fluid suitable for the afore-mentioned method is provided. The system includes an injection well 2 in communication with an oil storage stratum 3. The injection well 2 is provided with a sealed well-killing device therein. The injection well may be used as an independent injection well, or may double as an extraction well. The injection well and the extraction well may be two independent shafts, so as to allow simultaneous oil extraction and injection operations. Above the oil storage stratum 3 is a cover stratum 1, and below the oil storage stratum 3 is an understratum 5.

The oil storage stratum has a low initial temperature which cannot meet the requirements for injecting air for combustion, and some crude oil may be lighter. In the first stage, water vapor and ferrous sulfonate in vacuum gas oil are mixed to form a thermal fluid by means of a nozzle or other devices. The thermal fluid is injected into the oil storage stratum 3 through the injection well 2, and the temperature of the oil storage stratum 3 begins to rise. The ferrous sulfonate in vacuum gas oil is mixed and mutually dissolved with the crude oil, and then ferrous sulfonate is dissolved in the crude oil. Under the action of the catalyst and the water vapor, the crude oil undergoes a modification reaction to produce light products. Under the action of the temperature rise and the reaction, the viscosity of the crude oil is reduced, and finally, the crude oil with the viscosity reduced to a certain degree is extracted from the extraction well 4 by the displacement of the water vapor, and the temperature of the oil storage stratum 3 is increased to a value required for combustion in the second stage. In this process, there are heat losses from the oil storage stratum 3 to the cover stratum 1 and the understratum 5 inevitably. However, it is possible to ensure the initial temperature of the thermal fluid and the injection time to achieve the purposes of initial extraction and preheating. In the second stage, the extraction well 4 is closed, and the water vapor and air are mixed and in turn, injected into the oil storage stratum 3 through the injection well 2. A combustion reaction proceeds between air and the remaining crude oil that is difficult to be extracted by the conventional modification method in the first stage in the oil storage stratum 3, and the temperature and pressure of the oil storage stratum 3 are further increased to exceed critical points. At this time, oxygen and the crude oil may both be dissolved into the supercritical water, and react more quickly and fully in the dissolved state. Here, it needs to select an air injection rate and a ratio of the multielement thermal fluid according to the actual situation. The amount of oxygen should be insufficient as insufficient combustion may produce CO, which in turn produces H2. After the injection of the multielement thermal fluid in the second stage is stopped, the well is closed for a period of time to exhaust oxygen. In the third stage, the multielement thermal fluid formed by mixing the water vapor with methane is injected. After the water vapor is injected into the oil storage stratum 3, the temperature and the pressure are increased to exceed critical points, and methane may undergo a hydrothermal replacement reaction to produce H2. Under the action of ferrous sulfonate, H2, and supercritical water dissolved in the crude oil, the crude oil undergoes a modification reaction with the efficiency greatly improved, and the yield of light products is increased, and the yield of heavy products is reduced. Finally, the modified crude oil is extracted from the extraction well 4 by the displacement of the supercritical water, CO2 and the like. It is to be noted that if a water-soluble catalyst is used in the first stage, the catalyst may be used or not used in the third stage, because the efficiency of the reaction in the third stage may be high even without the catalyst, but the addition of the catalyst can increase the sweep range. With the heat absorption of the modification reaction and the heat dissipation of the oil storage stratum 3 to the cover stratum 1, the temperature may drop below the critical point when the crude oil is completely extracted. At this time, the second stage and the third stage can be repeated. 

What is claimed is:
 1. A heavy oil thermal recovery method based on staged injection of a supercritical multielement thermal fluid, comprising: S1, extracting light crude oil in an oil storage stratum in response to detecting that the oil storage stratum has an ignition temperature through preheating the oil storage stratum; S2, increasing a temperature of the oil storage stratum through igniting heavy oil in the oil storage stratum having the ignition temperature; and S3, injecting, sequence to heating the oil storage stratum to a required temperature, a multielement thermal fluid into the oil storage stratum, and extracting crude oil sequence to an operation of closing in.
 2. The heavy oil thermal recovery method based on staged injection of the supercritical multielement thermal fluid according to claim 1, further comprising: injecting a thermal fluid having steam and a catalyst into the oil storage stratum to heat the oil storage stratum to the ignition temperature or higher; and injecting a thermal fluid having steam and a flame-retardant gas to combust the oil storage stratum and increase the temperature of the oil storage stratum.
 3. The heavy oil thermal recovery method based on staged injection of the supercritical multielement thermal fluid according to claim 1, wherein the multielement thermal fluid comprises a mixture of water, a catalyst, and a hydrogen donor.
 4. The heavy oil thermal recovery method based on staged injection of the supercritical multielement thermal fluid according to claim 2, further comprising: repeatedly injecting, when the temperature of the oil storage stratum is lower than a reaction-requiring temperature, the thermal fluid having the steam and the catalyst to heat the temperature of the oil storage stratum to the reaction-requiring temperature.
 5. The heavy oil thermal recovery method based on staged injection of the supercritical multielement thermal fluid according to claim 2, wherein the multielement thermal fluid is doped with a combustion-supporting gas.
 6. The heavy oil thermal recovery method based on staged injection of the supercritical multielement thermal fluid according to claim 5, wherein the combustion-supporting gas comprises air, enriched oxygen, or pure oxygen.
 7. The heavy oil thermal recovery method based on staged injection of the supercritical multielement thermal fluid according to claim 2, wherein the catalyst comprises a water-soluble salt, an oil-soluble salt, or nanoparticles of a transition metal.
 8. The heavy oil thermal recovery method based on staged injection of the supercritical multielement thermal fluid according to claim 2, wherein the hydrogen donor comprises tetralin, methane, formic acid, methyl formate, dihydroanthracene, alcohols and naphthenic straight-run diesel, CO, or CH₄.
 9. The heavy oil thermal recovery method based on staged injection of the supercritical multielement thermal fluid according to claim 2, wherein the water is injected in a state as a mixture of low-temperature water, water vapor, or supercritical water.
 10. The heavy oil thermal recovery method based on staged injection of the supercritical multielement thermal fluid according to claim 1, wherein an injection well and an extraction well are formed as a single well, or the injection well and the extraction well are disposed separately. 